Polar wurtzite GaN can host surface phonon-polaritons (SPHPs) along its bulk surface and achieve sub-diffraction confinement with an ultralow optical loss and has emerged as a relevant technological material for infrared nanophotonics. Yet, few studies have reported on the temperature-dependent infrared dielectric functions, lattice vibration's influence on the hybrid phonon-polaritons, and the underlying physics that are largely unexplored. Herein, we perform the infrared spectroscopic ellipsometry (SE) measurements and multiscale simulations including first-principles and finite-difference time-domain (FDTD) to systematically study the infrared dielectric function at varying temperatures, phonon dynamics, and SPHPs in wurtzite GaN. SE experiments identify the reststrahlen band where the amplitude of ordinary dielectric function reduces significantly by a factor of 3.5 and the propagation length of SPHPs decreases by a factor of 4.18 as temperature increases from 250 to 800 K, suggesting the strong influence of lattice vibration on SPHPs. First-principles calculations confirm that the reststrahlen band for the ordinary dielectric function lies between the transverse and longitudinal E₁ phonon modes, while that of extraordinary dielectric function lies between the transverse and longitudinal A₁ phonon modes. FDTD simulations observe the localized surface phonon resonances in the nano-porous GaN thin films deposited on the sapphire substrate only for the transverse magnetic wave mode, which is consistent with the observation of extra dip in the measured pp-polarized reflection spectroscopy. This work provides a deep insight into lattice vibration influence on phonon dynamics and SPHPs in wurtzite GaN and helps engineer them in nanophotonic devices toward achieving better performance.

Microalgae are considered one of the most efficient and environmentally friendly ways for carbon dioxide fixation. The bubbles play an important role in analyzing the radiation transfer in photobioreactors during microalgae growth. Herein, Chlorella sp. and Scenedesmus obliquus were cultured in the airlift flat plate photobioreactor and evaluated for the temporal evolution of radiation characteristics. A one-dimensional model of bubbles on time-dependent radiation transfer in a photobioreactor was proposed, and it was well verified with the experimental result. The results indicated that with the increase of bubble volume fraction or the decrease of bubble radius, the local irradiance increased at the illuminated surface of the microalgal culture and was attenuated more rapidly along with the radiation transfer. The average specific growth rate of microalgae decreases as bubble volume fraction increases or bubble radius decreases. The volume fraction of 0.003 and a radius of 3.5 mm are the optimal operating conditions in this study for microalgae growth and carbon dioxide fixation. The presented analysis would facilitate the design and optimization of the optical and aeration configurations of photobioreactors for carbon dioxide fixation.

As the severity of environmental pollution continues to increase and ultralow emission standards are proposed, biomass power plants must implement additional processes to control SO₂ emission. Biomass ash can be utilized as a sorbent for flue gas desulfurization because of its strong alkalinity. In this study, the characteristics of SO₂ absorption in simulated flue gas using four types of typical biomass ashes were studied in fixed bed experiments. The results showed that the addition of water, the increase in water vapor, and the lower temperature were beneficial for SO₂ absorption. The main components of wheat straw ash are KCl and SiO₂, cotton stalk ash is rich in K₂O and calcium compounds, poplar bark ash has a considerable content of calcium compounds, and corncob ash contains large amounts of KCl and K₂O. Alkali substances, such as oxides or carbonates of potassium and calcium, play a crucial role in SO₂ absorption. The SO₂ removal effect of corncob ash was the best owing to the abundance of potassium oxides. Meanwhile, wheat straw ash performed worst in SO₂ removal due to the small amount of K₂O and Ca. The desulfurization products were mainly potassium and calcium sulfate.

Polar 4H-SiC nano-resonators can host localized surface phonon polaritons (SPhPs) with low optical loss and fully exploit light–matter interactions for promising nanophotonic applications such as surface-enhanced spectroscopies and thermal imaging. To expand the mid-infrared and infrared application spaces, a sound knowledge of temperature effect on infrared dielectric functions and SPhPs of 4H-SiC is required, yet it remains largely unexplored. Herein, we focus on exploiting the temperature influence on dielectric functions, hybridization of propagating and localized SPhPs, and tailed spectral radiation properties of 4H-SiC nanopillar arrays through spectroscopic ellipsometry (SE) measurements as well as multiscale simulations. The 4H-SiC crystal is grown using the physical vapor transport method, and SE experiments measure infrared dielectric functions at temperatures between 300 and 800 K. Finite-element electromagnetic simulations confirm the emerged Monopole and transverse dipoles (TD1 and TD2) resonance modes in 4H-SiC nano-resonators, which agrees with the literature experiment. At high temperatures with strong lattice vibration, the amplitudes of resonant optical absorption peaks gradually decrease and the linewidths broaden, accompanied by the weakened electric resonances. First-principles calculations show that the anharmonic phonon scattering strengthens and less optical phonons are coupled to incident photons as temperature increases. Moreover, the propagating and localized SPhPs’ hybridization and spectral radiation properties of 4H-SiC nanopillar arrays can be largely tailed by modifying the morphology and incident angle of light. This work provides physical insights into the temperature-induced spectral tuning of 4H-SiC nano-resonators and helps exploit their applications in the high-temperature working conditions.

Tantalum pentoxide (Ta₂O₅) has demonstrated promising applications in gate dielectrics and microwave communication devices with its intrinsically high dielectric constant and low dielectric loss. Although there are numerous studies on the dielectric properties of Ta₂O₅, few studies have focused on the influence of external environmental changes (i.e., temperature and pressure) on the dielectric properties and the underlying physics is not fully understood. Herein, we synthesize Ta₂O₅ thin films using the magnetron sputtering method, measure the ultraviolet-visible dielectric function at temperatures varying from 300 to 873 K by spectroscopic ellipsometry (SE), and investigate the temperature influence on the dielectric function from first principles. SE experiments observe that temperature has a nontrivial influence on the ultraviolet-visible dielectric function, accompanying the consistently decreased amplitude and increased broadening width for the dominant absorption peak. First-principles calculations confirm that the dominant absorption peak originates from the aggregated energy states near the valence band maximum (VBM) and conduction band minimum (CBM), and the theoretically predicted dielectric functions demonstrate good agreement with the SE experiments. Moreover, by performing first-principles molecular dynamics simulations, the finite-temperature dielectric function is predicted and its change trend with increasing temperature agrees overall with the SE measurements. This work explores the physical origins of temperature influence on the ultraviolet-visible dielectric function of Ta₂O₅, aimed at promoting its applications in the field of micro-/nanoelectronics.